Tool Calls

See what really happens when a model “uses a tool”

Speed
What the User Sees
Press Play to see a tool call in action
The Orchestration Loop
1
USER MESSAGE
Injected into context
2
SYSTEM PROMPT
Includes tool definitions as text
3
MODEL GENERATES
Outputs tool call JSON tokens
4
SYSTEM INTERCEPTS
Parses JSON, recognizes tool call
5
TOOL EXECUTES
Runs the actual function
6
RESULT INJECTED
Output added to context
7
MODEL CONTINUES
Generates natural language response
8
USER SEES ANSWER
The polished final response
System
Tool Def
Under the Hood
What the model actually outputs — one token at a time
Press Play to see the model generate a tool call token by token
Key Takeaways
  • Tool calling = structured text generation. The model produces JSON tokens one at a time, like writing a sentence.
  • The model doesn't “use” tools. It outputs text that a system interprets as a tool call.
  • Tool definitions are prompt text. They're injected into context like any other instruction.
  • The orchestration loop is the real magic. It's the system around the model that makes tool use work.
  • This is why tool calling can fail. If the model generates slightly wrong JSON, the tool call breaks. It's probabilistic.